CAPEC
76

An attacker manipulates inputs to the target software which the target software passes to file system calls in the OS. The goal is to gain access to, and perhaps modify, areas of the file system that the target software did not intend to be accessible.

Attack Execution Flow

Explore

Fingerprinting of the operating system:

In order to create a valid file injection, the attacker needs to know what the underlying OS is.

Attack Step Techniques

ID

Attack Step Technique Description

Environments

1

Port mapping. Identify ports that the system is listening on, and attempt to identify inputs and protocol types on those ports.

env-Local env-CommProtocol env-Peer2Peer env-ClientServer

2

TCP/IP Fingerprinting. The attacker uses various software to make connections or partial connections and observe idiosyncratic responses from the operating system. Using those responses, he attempts to guess the actual operating system.

Some fingerprinting techniques can be detected by operating systems or by network IDS systems because they leave the network connection half-open, or they do not belong to a valid, open connection.

Survey the Application to Identify User-controllable Inputs:

The attacker surveys the target application to identify all user-controllable inputs, possibly as a valid and authenticated user

Attack Step Techniques

ID

Attack Step Technique Description

Environments

1

Spider web sites for all available links, entry points to the web site.

env-Web

2

Manually explore application and inventory all application inputs

env-All

Outcomes

ID

type

Outcome Description

1

Success

The attacker develops a list of likely interesting path (application or OS related)

Security Controls

ID

type

Security Control Description

1

Detective

Monitor velocity of page fetching in web logs. Humans who view a page and select a link from it will click far slower and far less regularly than tools. Tools make requests very quickly and the requests are typically spaced apart regularly (e.g. 0.8 seconds between them).

2

Detective

Create links on some pages that are visually hidden from web browsers. Using IFRAMES, images, or other HTML techniques, the links can be hidden from web browsing humans, but visible to spiders and programs. A request for the page, then, becomes a good predictor of an automated tool probing the application.

3

Preventative

Actively monitor the application and either deny or redirect requests from origins that appear to be automated.

4

Detective

Monitor velocity of feature activations (non-web software). Humans who activate features (click buttons, request actions, invoke APIs, etc.) will do so far slower and far less regularly than tools. Tools make requests very quickly and the requests are typically spaced apart regularly (e.g. 0.8 seconds between them).

Experiment

Vary inputs, looking for malicious results:

Depending on whether the application being exploited is a remote or local one the attacker crafts the appropriate malicious input containing the path of the targeted file or other file system control syntax to be passed to the application

The attacker injects context-appropriate malicious file system control syntax to cause the application to create, delete a targeted file.

env-All

5

The attacker injects context-appropriate malicious file path in order to manipulate the meta-data of the targeted file.

env-All

6

The attacker injects context-appropriate malicious file system control syntax in order to manipulate the meta-data of the targeted file.

env-All

Outcomes

ID

type

Outcome Description

1

Success

The software performs an action the attacker desires. This might be displaying information, storing information in a file, delete a file or some other malicious activity.

Security Controls

ID

type

Security Control Description

1

Detective

Use a system that logs file modification and/or access.

2

Preventative

Make the application run in a low-privileged mode to prevent such attack to access important files.

Attack Prerequisites

Program must allow for user controlled variables to be applied directly to the filesystem

Typical Likelihood of Exploit

Likelihood: High

Methods of Attack

Injection

API Abuse

Modification of Resources

Examples-Instances

Description

An example of using path traversal to attack some set of resources on a web server is to use a standard HTTP request

http://example/../../../../../etc/passwd

From an attacker point of view, this may be sufficient to gain access to the password file on a poorly protected system. If the attacker can list directories of critical resources then read only access is not sufficient to protect the system.

Attacker Skills or Knowledge Required

Skill or Knowledge Level: Low

To identify file system entry point and execute against an overprivileged system interface

Solutions and Mitigations

Design: Enforce principle of least privilege.

Design: Ensure all input is validated, and does not contain file system commands

Design: Run server interfaces with a non-root account and/or utilize chroot jails or other configuration techniques to constrain privileges even if attacker gains some limited access to commands.

Design: For interactive user applications, consider if direct file system interface is necessary, instead consider having the application proxy communication.

Implementation: Perform testing such as pentesting and vulnerability scanning to identify directories, programs, and interfaces that grant direct access to executables.